Fix CI: Remove redundant toolchain input from dtolnay/rust-toolchain@stable

The dtolnay/rust-toolchain action already specifies the toolchain version
in the action reference (@stable). Adding toolchain: stable as an input
was causing 'toolchain is a required input' errors.

Fixed in:
- ci.yml
- release.yml
- crates-publish.yml

.github/workflows/ci.yml

@@ -18,7 +18,6 @@ jobs:
       - uses: actions/checkout@v4
       - uses: dtolnay/rust-toolchain@stable
         with:
-          toolchain: stable
           components: clippy, rustfmt
       - uses: Swatinem/rust-cache@v2
       - name: Check formatting
@@ -35,8 +34,6 @@ jobs:
     steps:
       - uses: actions/checkout@v4
       - uses: dtolnay/rust-toolchain@stable
-        with:
-          toolchain: stable
       - uses: Swatinem/rust-cache@v2
       - name: Run tests
         run: cargo test --all-features
@@ -52,8 +49,6 @@ jobs:
     steps:
       - uses: actions/checkout@v4
       - uses: dtolnay/rust-toolchain@stable
-        with:
-          toolchain: stable
       - uses: Swatinem/rust-cache@v2
       - name: Build
         run: cargo build --release
@@ -65,8 +60,6 @@ jobs:
     steps:
       - uses: actions/checkout@v4
       - uses: dtolnay/rust-toolchain@stable
-        with:
-          toolchain: stable
       - uses: Swatinem/rust-cache@v2
       - name: Build docs
         run: cargo doc --no-deps